1. Probably we can't compete with Intelli-J on the
android development.

Indeed, unless several people are ready to commit to work full time
on it for several monthes.

2. We can improve Eclipse WTP to improve the web
development experience. This is where we lost part of the
users, in favor of webstorm and netbeans.

I fully agree. The state of JS edition got improved, but the HTML
and CSS editors are still far behind many other ones in term of
usability and features. However, this would require more resources
on WTP, more people to review the various incoming patches (
https://git.eclipse.org/r/#/q/status:open+project:sourceediting/webtools.sourceediting
) or if the current committers cannot commit on reviewing the
patches fast enough, we could recruit interested parties (such as
you and Gauthier as committers).

3. We could gain users proposing a new offer: a lightweight
Eclipse IDE integrated with LSP-editors and cloud IDEs.

- Eclipse Two is a good point to start, where we
could plug CEF, (or Electron #?)
and LSP4E
based editors.

I'm currently only considering Eclipse IDE, not the other ones.
LSP4E is only targetting Eclipse IDE.

- Also, Chromium Embedded will give us a chance to
re-think E4 RCP applications. (A chromium-based framework,
which can run RCP Plugins?)

I don't think users have left Eclipse IDE because it's not based on
CEF nor Electron nor Chromium Embedded. They left because of missing
or clunky high-level features that are better supported by
competitors. It's not at all a matter of technology nor design IMHO,
but "only" a matter of implementing and placing the right features
at the right place and the right time in the user-stories.
People typically complain about completion being suboptimal, or the
need to use keystrokes or certain characters to trigger completion,
the lack of some refactorings, the inconsistency between Maven and
JDT model... none of this is an issue that is related to the core
architecture.